Light emitting diode

ABSTRACT

A light emitting diode includes a substrate, a first semiconductor layer, an active layer, a second semiconductor layer, and at least one transparent conductive layer. The transparent conductive layer comprises of a carbon nanotube structure.

RELATED APPLICATIONS

This application is related to applications entitled, “METHOD FORFABRICATING LIGHT EMITTING DIODE”, filed **** (Atty. Docket No.US23023).

BACKGROUND

1. Technical Field

The present disclosure relates to a light emitting diode (LED).

2. Description of the Related Art

LEDs are semiconductors that convert electrical energy into light.Compared to conventional light sources, the LEDs have higher energyconversion efficiency, higher radiance (i.e., they emit a largerquantity of light per unit area), longer lifetime, higher responsespeed, and better reliability. At the same time, LEDs generate lessheat. Therefore, LED modules are widely used in particular as asemiconductor light source in conjunction with imaging optical systems,such as displays, projectors, and so on.

Referring to FIG. 6, a typical LED 10, according to the prior artincludes a substrate 110, a GaN bumper layer 120, an N-type GaN layer132, an active layer 134, a P-type GaN layer 136, and a transparentcontact layer 140. The GaN bumper layer 120, the N-type GaN layer 132,the active layer 134, the P-type GaN layer 136, and the transparentcontact layer 140 are stacked on the substrate 110. The LED 10 furtherincludes a transparent conductive layer 150, a first electrode 142, anda second electrode 144. The first electrode 142 is disposed on theN-type semiconductor layer 132. The transparent conductive layer 150 andthe second electrode 144 are disposed on the transparent contact layer140. The transparent conductive layer 150 is made of indium tin oxide(ITO) and the ITO is sputtered on an area of the transparent contactlayer 140. Due to the net structure of the ITO layer, the lateraldistribution of current applied on the transparent conductive layer 150is uniform, thereby improving the extraction efficiency of light of theLED. However, the ITO layer has some faults, such as low mechanicalstrength and resistance distribution. Furthermore, the transparency ofthe ITO layer may be decreased in humid environments and the ITO layermay absorb some of the light emitted by the active layer 134 when theITO fully covers the P-type semiconductor layer 136.

What is needed, therefore, is a light emitting diode, which can overcomethe above-described shortcomings.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the embodiments can be better understood with referenceto the following drawings. The components in the drawings are notnecessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the embodiments. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 is a schematic, partial exploded view of a light emitting diodeaccording to an embodiment.

FIG. 2 is a schematic view of the light emitting diode of FIG. 1.

FIG. 3 is a scanning electron microscope (SEM) image of a carbonnanotube film used in the light emitting diode of FIG. 1.

FIG. 4 is a schematic view of a light emitting diode according to ananother embodiment.

FIG. 5 is a schematic view of a light emitting diode according to anembodiment.

FIG. 6 is schematic, cross-sectional view of a typical light emittingdiode according to prior art.

DETAILED DESCRIPTION

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” embodiment in this disclosure are not necessarily tothe same embodiment, and such references mean at least one.

Referring to FIG. 1 and FIG. 2, a first embodiment of a light emittingdiode (LED) 20 includes a substrate 210, a first semiconductor layer232, an active layer 234, a second semiconductor layer 236, a firstelectrode 242, a second electrode 244, a transparent conductive layer250, and a static electrode 240. The first semiconductor layer 232, theactive layer 234, the second semiconductor layer 234 are orderly stackedon the substrate 210. The first electrode 242 is electrically connectedto the first semiconductor layer 232. The transparent conductive layer250 is disposed on the top surface of the second semiconductor layer 236and electrically connected to the second semiconductor layer 236. Thestatic electrode 240 is interposed between the second semiconductorlayer 236 and the transparent conductive layer 250. The second electrode244 is disposed on the top surface of the transparent conductive layer250 and electrically connected to the transparent conductive layer 250.

The substrate 210 may have a thickness of about 300 microns (μm) toabout 500 μm and a transparent plate for supporting the other elements,such as the first and second semiconductor layers 232, 236. Thesubstrate 210 may be made of sapphire, gallium arsenide, indiumphosphate, silicon nitride, gallium nitride, zinc oxide, aluminumsilicon nitride, silicon carbon, or their combinations. In oneembodiment, the substrate 210 is made of sapphire and has a thickness of400 μm.

The first semiconductor layer 232, the active layer 234, and the secondsemiconductor layer 236 can be stacked on the substrate 210 via aprocess of metal organic chemical vapor deposition (MOCVD).

The first semiconductor layer 232 has a thickness of about 1 μm to about5 μm. The second semiconductor layer 236 has a thickness of about 0.1 μmto about 3 μm. When the first semiconductor layer 232 is an N-typesemiconductor, the second semiconductor layer 236 is a P-typesemiconductor, and vice versa. In one embodiment, the firstsemiconductor layer 232 is an N-type semiconductor and the secondsemiconductor layer 236 is a P-type semiconductor. The firstsemiconductor layer 232 has a step-shaped structure and includes a firstsurface 262 and a second surface 264 located on the same side as thefirst surface 262. The first surface 262 and the second surface 264 havedifferent heights and form a step-shaped structure. The active layer 234and the second semiconductor layer 236 are arranged on the first surface262.

The first semiconductor layer 232 is configured to provide electrons,and the second semiconductor layer 236 is configured to providecavities. When a voltage is applied to the first and secondsemiconductor layers 232, 236, the electrons can flow into the secondsemiconductor 236 and incorporate with the cavities, thereby emittinglight. The first semiconductor layer 232 may be made of N-type galliumnitride, N-type gallium arsenide, or N-type copper phosphate. The secondsemiconductor layer 236 may be made of P-type gallium nitride, P-typegallium arsenide, or P-type copper phosphate. In one embodiment, thefirst semiconductor layer 232 is made of N-type gallium nitride and hasa thickness of 2 μm, and the second semiconductor layer 236 is made ofP-type gallium nitride and has a thickness of 0.3 μm.

The active layer 234, in which the electrons fill the holes, has athickness of about 0.01 μm to about 0.6 μm. The active layer 234 is aphoton exciting layer and can be one of a single quantum well layer ormultilayer quantum well films. The active layer 140 can be made ofGaInN, AlGaInN, GaSn, AlGaSn, GaInP, or GaInSn. In one embodiment, theactive layer 234 has a thickness of 0.3 μm and includes one layer ofGaInN stacked with a layer of GaN.

The static electrode 240 is formed on the top surface of the secondsemiconductor layer 236. The static electrode 240 may be a P-typeelectrode or an N-type electrode and is a same type as the secondsemiconductor layer 236. Therefore, in one embodiment, the staticelectrode 236 is a P-type electrode. Understandably, the staticelectrode 236 can function as a reflection layer. The static electrode236 can have one or more layers of metal and may be made of titanium,aluminum, nickel, gold, or any combinations thereof In one embodiment,the static electrode 236 has two layers. One layer is made of titaniumand has a thickness of 15 nanometers (nm). The other layer is made ofgold and has a thickness of 100 nm. The static electrode 240 is formedon the second semiconductor layer 236 via a process of physical vapordeposition, such as electron evaporation, vacuum evaporation, ionsputtering, or the like.

Further, a functioning layer may be formed between the substrate 210 andthe first semiconductor layer 232. The functioning layer may be one ormore of a buffer layers, a reflective layer, and a photon crystalstructure. The buffer layer is configured to improve epitaxial growthand decrease lattice mismatch. The buffer layer may be made of GaN, AlN,or the like. The reflective layer is configured to change thetransmission route of the light to improve extraction efficiency oflight in the LED. The reflective layer may be made of silver, aluminum,rhodium, or the like. The photon crystal structure is configured toimprove extraction efficiency of light and may be made of silicon,indium tin oxide, carbon nanotube, or the like. In one embodiment, onlythe buffer layer 220 is formed on the substrate 210 and is made of GaN.The buffer layer 220 has a thickness of about 20 nm to about 50 nm.

The transparent conductive layer 250 includes a carbon nanotubestructure. The transparent conductive layer 250 can be directly appliedto the top surface of the second semiconductor layer 236 and the staticelectrode 240. The transparent conductive layer 250 may only cover theexposed surface of the second semiconductor layer 236 and fully orpartly cover both the top surface of the static electrode 240 and thesecond semiconductor layer 236. In one embodiment, the transparentconductive layer 250 fully covers both the second semiconductor layer236 and the static electrode 240. The carbon nanotube structure mayinclude at least one carbon nanotube film and/or a number of carbonnanotube wires. The use of all types of carbon nanotube films and/orcarbon nanotube wires is envisioned to be employed by the transparentconductive layer 250. There is no particular restriction on thethickness of the carbon nanotube structure and it may be appropriatelyselected depending on the purpose, and may be, for example, greater than0.5 nm, and more specifically from about 0.5 μm to 200 μm.

The carbon nanotube structure can include one or more layers of carbonnanotube films. When the carbon nanotube structure includes a number ofcarbon nanotube films, the carbon nanotube films are stacked on top ofeach other. The carbon nanotube structure can employ more carbonnanotube films to increase the tensile strength of the carbon nanotubecomposite 100. The carbon nanotube film has a thickness in anapproximate range from about 0.5 nm to about 100 mm. The carbonnanotubes films may have a free-standing structure. The film structurebeing supported by itself and does not require a substrate to maintainits structural integrity. As an example, a corner of the carbon nanotubefilm can be lifted without resulting in damage to the entire structure.

Referring to FIG. 3, the carbon nanotube films each are formed by thecarbon nanotubes, orderly or disorderly, and has substantially a uniformthickness. Ordered carbon nanotube films include films where the carbonnanotubes are arranged along a primary direction. Examples include filmswherein the carbon nanotubes are arranged approximately along a samedirection or have two or more sections within each of which the carbonnanotubes are arranged approximately along a same direction (differentsections can have different directions). In the ordered carbon nanotubefilms, the carbon nanotubes are oriented along the same preferredorientation and approximately parallel to each other. A film can bedrawn from a carbon nanotube array, to form the ordered carbon nanotubefilm, namely a drawn carbon nanotube film. Examples of drawn carbonnanotube film are taught by U.S. Pat. No. 7,045,108 to Jiang et al., andWO 2007015710 to Zhang et al. The drawn carbon nanotube film includes aplurality of successive and oriented carbon nanotubes joined end-to-endby van der Waals attractive force therebetween. The drawn carbonnanotube film is a free-standing film. The carbon nanotube film can betreated with an organic solvent to increase the mechanical strength andtoughness of the carbon nanotube film and reduce the coefficient offriction of the carbon nanotube film. A thickness of the carbon nanotubefilm can range from about 0.5 nanometers to about 100 micrometers.

The ordered carbon nanotube film may be a pressed carbon nanotube filmhaving a number of carbon nanotubes arranged along a same direction. Thecarbon nanotubes in the pressed carbon nanotube film can rest upon eachother. Adjacent carbon nanotubes are attracted to each other andcombined by van der Waals attractive force. An angle between a primaryalignment direction of the carbon nanotubes and a surface of the pressedcarbon nanotube film is 0 degree to approximately 15 degrees. Thegreater the pressure applied, the smaller the angle formed. Thethickness of the pressed carbon nanotube film ranges from about 0.5 nmto about 1 mm. Examples of pressed carbon nanotube film are taught by USapplication 20080299031A1 to Liu et al.

The disordered carbon nanotube film comprises carbon nanotubes arrangedin a disorderly fashion. Disordered carbon nanotube films includerandomly aligned carbon nanotubes. When the disordered carbon nanotubefilm comprises of a film wherein the number of the carbon nanotubesaligned in every direction is substantially equal, the disordered carbonnanotube film can be isotropic. The disordered carbon nanotubes can beentangled with each other and/or are substantially parallel to a surfaceof the disordered carbon nanotube film. The disordered carbon nanotubefilm may be a flocculated carbon nanotube film. The flocculated carbonnanotube film can include a plurality of long, curved, disordered carbonnanotubes entangled with each other. The carbon nanotubes can besubstantially uniformly dispersed in the flocculated carbon nanotubefilm. Adjacent carbon nanotubes are attracted by van der Waalsattractive force to form an entangled structure with micropores definedtherein. It is understood that the flocculated carbon nanotube film isvery porous. Sizes of the micropores can be less than 10 μm. Due to thecarbon nanotubes in the flocculated carbon nanotube film being entangledwith each other, the carbon nanotube structure employing the flocculatedcarbon nanotube film has excellent durability, and can be fashioned intodesired shapes with a low risk to the integrity of the flocculatedcarbon nanotube film. The thickness of the flocculated carbon nanotubefilm can range from about 0.5 nm to about 1 millimeter (mm).

The disordered carbon nanotube film may be a pressed carbon nanotubefilm having a number of carbon nanotubes arranged along differentdirections. The pressed carbon nanotube film can be a free-standingcarbon nanotube film. When the carbon nanotubes in the pressed carbonnanotube film are arranged along different directions, the pressedcarbon nanotube film can be isotropic. As described above, the thicknessof the pressed carbon nanotube film ranges from about 0.5 nm to about 1mm. Examples of pressed carbon nanotube film are taught by USapplication 20080299031A1 to Liu et al.

Length and width of the carbon nanotube film can be arbitrarily set asdesired. A thickness of the carbon nanotube film is in a range fromabout 0.5 nm to about 100 μm. The carbon nanotubes in the carbonnanotube film can be single-walled, double-walled, multi-walled carbonnanotubes, and combinations thereof. Diameters of the single-walledcarbon nanotubes, the double-walled carbon nanotubes, and themulti-walled carbon nanotubes can, respectively, be in the approximaterange from about 0.5 nm to about 50 nm, about 1 nm to about 50 nm, andabout 1.5 nm to about 50 nm.

The carbon nanotube structure include a number of carbon nanotube wires.The carbon nanotube wires may be arraigned side by side on the topsurface of the second semiconductor layer or may be weaved into a carbonnanotube layer. The weaved carbon nanotube layer is applied to thesecond semiconductor layer. The carbon nanotube wire includes untwistedcarbon nanotube wire and twisted carbon nanotube wire. The untwistedcarbon nanotube wire includes a number of carbon nanotubes parallel toeach other. The twisted carbon nanotube wire includes a number of carbonnanotube helically twisted along a longitudinal axis of the twist carbonnanotube wire.

The untwisted carbon nanotube wire can be formed by treating the drawncarbon nanotube film with an organic solvent. The drawn carbon nanotubefilm is treated by applying the organic solvent to the carbon nanotubefilm while being free to bundle. After being soaked by the organicsolvent, the adjacent paralleled carbon nanotubes in the drawn carbonnanotube film will bundle together, due to the surface tension of theorganic solvent when the organic solvent volatilizing, and thus, thedrawn carbon nanotube film will be shrunk into untwisted carbon nanotubewire. The carbon nanotubes of the untwisted carbon nanotube wires aresubstantially parallel to each other along the longitudinal axis of theuntwisted carbon nanotube wires. Examples of the untwisted carbonnanotube wire are taught by U.S. Pat. No. 7,045,108 to Fan et al. and USpublication No. 20070166223 to Fan et al.

The twisted carbon nanotube wire can be formed by twisting a drawncarbon nanotube film by using a mechanical force to turn the two ends ofthe drawn carbon nanotube film in opposite directions. Further, thetwisted carbon nanotube wire can be treated by applying the organicsolvent. After applying the organic solvent, the adjacent carbonnanotubes in the twisted carbon nanotube film will bundle together, dueto the surface tension of the organic solvent when the organic solventvolatilizing, and thus, the twisted carbon nanotube wire may have lessspecific surface area, and larger density and strength than an untreatedtwisted carbon nanotube wire.

The transparent conductive layer 250 may be made by steps of forming ametal layer (not shown) on the carbon nanotube structure and heating themetal layer in a temperature of about 300 degrees centigrade to about500 degrees centigrade for about 3 minutes to about 10 minutes. Themetal layer may be a single-layer structure or a multi-layeredstructure. In one embodiment, the metal layer includes a nickel layerstacked with a gold layer. The nickel layer has a thickness of about 2nm. The gold layer has a thickness of 5 nm. Since the metal layerdecreases in thickness because of the heating, the metal molecule of themetal layer can be melted and can aggregate into a number of metalparticles by surface tension. The carbon nanotube structure has aplurality of micropores between adjacent carbon nanotubes of the carbonnanotube structure. These metal particles uniformly disperse in themicropores of the carbon nanotube structure to form a composite film.The composite film, which functions as the transparent conductive layer250, has better electrical conductivity than the pure carbon nanotubestructure, thereby improving current injection efficiency and electricalcontact between the carbon nanotube structure and the static electrode240, the first electrode 242, and the second semiconductor layer 236.

In one embodiment, two drawn carbon nanotube films are coated on thesecond semiconductor layer 236 and the static electrode 340. An anglebetween the primary directions of the two drawn carbon nanotube filmsranges from about 0 degrees to about 90 degrees. In one embodiment, theprimary directions of the two drawn carbon nanotube films areperpendicular to each other.

The first electrode 242 can be deposited on the transparent conductivelayer 250 via physical vapor deposition and may have single-layerstructure or multi-layered structure. The first electrode 242 can bemade of titanium or gold. In one embodiment, the first electrode 242includes two layers, one layer is titanium and has a thickness of 15 nmand another layer is gold and has a thickness of 200 nm. At least aportion of the carbon nanotube structure is located between the staticelectrode 240 and the first electrode 242. The first electrode 242 maybe P-type or N-type electrode and is the same type as the staticelectrode 240 and the second semiconductor layer 236. Since the staticelectrode 240 is made of P-type material, the first electrode 242 is aP-type electrode. When the LED 20 has the static electrode 240, thefirst electrode 242 should be located above the static electrode 240.When the LED has no static electrode 240, the first electrode 242 can belocated at any position on the transparent conductive layer 250. In oneembodiment, since the LED employs the static electrode 240, the firstelectrode 242 is located above the static electrode 242. The firstelectrode 242 and the static electrode 240 function together as the

P-type electrode of the LED. The second electrode 244 is a same polaritytype with the first semiconductor layer 236 and may be made of N-typematerial. The second electrode 244 is deposited on the second surface264 of the first semiconductor layer 236. The second electrode 244 has asame structure as the first electrode 242 and includes a titanium layerand a gold layer stacked on the titanium layer. The titanium layer has athickness of about 15 nm and the gold layer has a thickness of about 200nm. The method of depositing the second electrode 244 can be the same asthat of the first electrode 242. The first and second electrodes 242,244 can be deposited at the same time.

Referring to FIG. 4, in one embodiment, an LED 30 includes a substrate310, a buffer layer 320, a first semiconductor layer 332, an activelayer 334, a second semiconductor layer 336, a first electrode 342, asecond electrode 344, a transparent conductive layer 350, and a staticelectrode 340. The buffer layer 320, the first semiconductor layer 332,the active layer 334, the second semiconductor layer 336 are orderlystacked on the substrate 310.

The first semiconductor layer 332 includes a first surface 362 and asecond surface 364 located on the same side as the first surface 362.The first surface 362 and the second surface 364 have different heightsand form a stepped structure. The active layer 334 and the secondsemiconductor layer 336 are disposed on the first surface 362. Thetransparent conductive layer 350 is disposed on the second surface 364of the first semiconductor layer 332 and electrically connected to thefirst semiconductor layer 332. Further, the static electrode 340 isinterposed between the first semiconductor layer 332 and the transparentconductive layer 350. The first electrode 342 is disposed on the topsurface of the transparent conductive layer 350 and electricallyconnected to the transparent conductive layer 350. The second electrode344 is electrically connected to the second semiconductor layer 336.

Referring to FIG. 5, in one embodiment, an LED 40 includes a substrate410, a buffer layer 420, a first semiconductor layer 432, an activelayer 434, a second semiconductor layer 436, a first electrode 442, asecond electrode 444, a first transparent conductive layers 450, asecond transparent conductive layer 452, and a first static electrode440, a second static electrode 446. The buffer layer 420, the firstsemiconductor layer 432, the active layer 434, the second semiconductorlayer 436 are orderly stacked on the substrate 310.

The first semiconductor layer 432 includes a first surface 462 and asecond surface 464 located on the same side a the first surface 462. Thefirst surface 462 and the second surface 464 have different heights andform a stepped structure. The second transparent conductive layer 452 ismounted on the second semiconductor layer 436, and the first transparentconductive layer 450 is mounted on the second surface 464 of the firstsemiconductor layer 432. Further, the first static electrode 440 islocated between the second semiconductor layer 436 and the secondtransparent conductive layer 452, and the second electrode 444 isdisposed on the top surface of the second transparent conductive layer452. The second static electrode 446 is interposed between the firstsemiconductor layer 436 and the first transparent conductive layer 450,and the first electrode 442 is disposed on the top surface of the firsttransparent conductive layer 450.

Since the carbon nanotubes have better electrical conductivity andmechanical strength than conventional material, such as indium tinoxide, the carbon nanotube structure has better electrical conductivityand mechanical strength, thereby improving power efficiency and lifespan. Further, the carbon nanotube structure is stays transparent invaried humid environments. Therefore less of the light emitted by theactive layer is absorbed. Thus, the LED has good extraction efficiencyin comparison with the typical LED.

It is to be understood, however, that even though numerouscharacteristics and advantages of the present embodiments have been setforth in the foregoing description, together with details of thestructures and functions of the embodiments, the disclosure isillustrative only, and changes may be made in detail, especially inmatters of shape, size, and arrangement of parts within the principlesof the disclosure to the full extent indicated by the broad generalmeaning of the terms in which the appended claims are expressed.

1. A light emitting diode, comprising: a substrate, a firstsemiconductor layer, an active layer, a second semiconductor layer, andat least one transparent conductive layer, the transparent conductivelayer comprises a carbon nanotube structure.
 2. The light emitting diodeof claim 1, wherein the carbon nanotube structure is a free-standingstructure.
 3. The light emitting diode of claim 1, wherein thetransparent conductive layer comprises the carbon nanotube structure anda plurality of metal particles, the metal particles are dispersed in thecarbon nanotube structure to form a composite layer.
 4. The lightemitting diode of claim 1, wherein the carbon nanotube structurecomprises a plurality of carbon nanotubes.
 5. The light emitting diodeof claim 1, wherein the carbon nanotube structure comprises at least onecarbon nanotube film, the carbon nanotube film comprises a plurality ofcarbon nanotubes joined by van der Waals force.
 6. The light emittingdiode of claim 1, wherein the carbon nanotube structure comprises adrawn carbon nanotube film, the drawn carbon nanotube film comprises aplurality of carbon nanotubes approximately parallel to each other. 7.The light emitting diode of claim 6, wherein the carbon nanotubestructure comprises two drawn carbon nanotube films, an angle betweenaligned directions of the drawn carbon nanotube films is approximately90 degrees.
 8. The light emitting diode of claim 1, wherein the carbonnanotube structure comprises a carbon nanotube film, the carbon nanotubefilm comprises a plurality of carbon nanotubes, the carbon nanotubes areentangled with one another.
 9. The light emitting diode of claim 1,wherein the carbon nanotube structure comprises a plurality of twistedcarbon nanotube wires, each of the twisted carbon nanotube wirescomprise a plurality of carbon nanotubes, the carbon nanotubes helicallywrap around the longitudinal axis of the twisted carbon nanotube wires.10. The light emitting diode of claim 1, wherein the carbon nanotubestructure comprises a plurality of untwisted carbon nanotube wires, eachof the untwisted carbon nanotube wires comprise a plurality of carbonnanotubes, the carbon nanotubes are substantially parallel to each otherand the longitudinal axis of the untwisted carbon nanotube wires. 11.The light emitting diode of claim 1, further comprising a staticelectrode formed between the second semiconductor layer and thetransparent conductive layer.
 12. The light emitting diode of claim 1,further comprising a buffer layer located between the substrate and thefirst semiconductor layer.
 13. The light emitting diode of claim 1,further comprising a reflecting layer located between the substrate andthe first semiconductor layer.
 14. The light emitting diode of claim 1,further comprising a photon crystal structure located between thesubstrate and the first semiconductor layer.
 15. A light emitting diodecomprising: a substrate, a first semiconductor layer, an active layer, asecond semiconductor layer, a first transparent conductive layer, and asecond transparent conductive layer; the first semiconductor layerincludes a first surface and a second surface; the active layer and thesecond semiconductor layer are formed on the first surface; the secondtransparent conductive layer is mounted on an top surface of the secondsemiconductor layer; and the first transparent conductive layer ismounted on the second surface of the first semiconductor layer; whereineach of the first and second transparent conductive layers comprise of acarbon nanotube structure.
 16. The light emitting diode of claim 15,wherein the first surface and the second surface of the firstsemiconductor layer are located on different planes and form astep-shaped structure.
 17. A light emitting diode comprising: asubstrate, a first semiconductor layer, an active layer, a secondsemiconductor layer, and a transparent conductive layer; the firstsemiconductor layer comprises a first surface and a second surface, andthe first and second surface are located on same side of the firstsemiconductor layer; the active layer and the second semiconductor layerare disposed on the first surface; the transparent conductive layer isdisposed on the second surface of the first semiconductor layer andelectrically connected to the first semiconductor layer; and thetransparent conductive layer comprises of a carbon nanotube structure.18. The light emitting diode of claim 17, further comprising a firstelectrode and a second electrode, the first electrode is disposed on atop surface of the transparent conductive layer, and the secondelectrode is disposed on the second semiconductor layer.